The modem trend in the design and implementation of hearing devices is focusing to a large extent on reducing the physical size of the hearing device. Miniaturization of hearing device components is becoming increasingly feasible with rapid technological advances in the fields of power supplies, sound processing electronics and micro-mechanics. The demand for smaller and less conspicuous hearing devices continues to increase as a larger portion of our population ages and faces hearing loss. Those who face hearing loss also encounter the accompanying desire to avoid the stigma and self consciousness associated with this condition. As a result, smaller hearing devices which are cosmetically less visible are increasingly sought after.
Hearing device technology has progressed rapidly in recent years. First generation hearing devices were primarily of the Behind-The-Ear (BTE) type, where an externally mounted device was connected by an acoustic tube to a molded shell placed within the ear. With the advancement of component miniaturization, modern hearing devices rarely use this Behind-The-Ear technique, focusing primarily on one of several forms of an In-The-Canal hearing device. Three main types of In-The-Canal hearing devices are routinely offered by audiologists and physicians. In-The-Ear (ITE) devices rest primarily in the concha of the ear and have the disadvantages of being fairly conspicuous to a bystander and relatively bulky to wear. Smaller In-The-Canal (ITC) devices fit partially in the concha and partially in the ear canal and are less visible but still leave a substantial portion of the hearing device exposed. Recently, Completely-In-The-Canal (CIC) hearing devices have come into greater use. As the name implicates, these devices fit deep within the ear canal and are essentially hidden from view from the outside.
In addition to the obvious cosmetic advantages these types of in-the-canal devices provide, they also have several performance advantages that larger, externally mounted devices do not offer. Placing the hearing device deep within the ear canal and proximate to the tympanic membrane (ear drum) improves the frequency response of the device, reduces distortion due to jaw extrusion, reduces the occurrence of the occlusion effect and improves overall sound fidelity.
The shape and structure (morphology) of the ear canal varies from person to person. However, certain characteristics are common to all individuals. When viewed in the transverse plane, the path of the ear canal is extremely irregular, having several sharp bends and curves. It is these inherent structural characteristics that create problems for the acoustic scientist and the hearing device designer.
For general discussion purposes, the ear canal can be broken into three main segments. The external and medial segments are both surrounded by a relatively soft cartilaginous tissue. The external segment is largely visible from the outside and represents the largest cavity of the ear canal. The innermost segment of the ear canal, closest to the tympanic membrane, is surrounded by a denser bony material and is covered with only a thin layer of soft tissue. The presence of this bony material allows for little expansion to occur in this region compared with the cartilaginous regions of the ear canal. In addition to being surrounded by cartilage rather than bone, these areas are covered with a substantially thicker tissue layer. Since there is less cushion, pressure exerted by a hearing device on the inner bony region of the canal can lead to discomfort and/or pain, especially when a deep insertion technique is used.
Since the morphology of the ear canal varies so greatly from person to person, hearing aid manufacturers and audiologists use custom manufactured devices in order to precisely fit the dimensions of a user's ear canal. This frequently requires impressions of the user's ear canal to be taken. The resulting mold is then used to fabricate a rigid hearing device shell. This process is both expensive and time consuming and the resulting rigid device shell does not perform well during the deformations of the ear canal that occur during normal jaw movement. In order to receive a properly fit hearing device, the user typically has to make several trips to the audiologist for reshaping and resizing. Even after the best possible fit is obtained, the rigid shell rarely provides comfortable hearing enhancement at all times.
Because the resulting hearing aid device shell is typically formed from a hard acrylic material, discomfort to the user is increased when worn for extended periods of time. The inability of the hard shell to conform to normal ear canal deformations can cause it to become easily dislodged from its proper position. Consequently, the quality of the hearing enhancement suffers. Furthermore, due to the added manufacturing costs, it is desirable to utilize a hearing device that is at least partially formed from an off-the-shelf or pre-formed component readily available to the audiologist or physician.
While the performance of CIC hearing devices are generally superior to other larger and less sophisticated devices, several problems remain. Complications typically arise due to the small size of CIC hearing devices and the depth that they are inserted into a user's ear canal.
Because a CIC hearing device forms an essentially air tight seal between the tip of the hearing device and the walls of the ear canal, discomfort to a user is common. In particular, this acoustic seal prevents the equalization of pressure between the internal chamber formed between the tympanic membrane and the hearing device, and the ambient environment. Due to the sensitivity of the tympanic membrane, even small pressure differentials can cause severe discomfort.
Due to their small size and positioning within the ear canal, CIC hearing devices can cause handling problems, making insertion and removal by a user difficult and cumbersome and often lead to damage to the hearing device. In larger, BTE, or ITC hearing devices, the size of the device makes it unnecessary to incorporate a retrieval mechanism into its structure, i.e., the wearer normally will not have any difficulty grasping the device in order to remove it. But in smaller hearing devices, such as a CIC device, retrieval cords and other extraction tools become a necessary addition in order to allow for easy and safe removal by the wearer.
U.S. Pat. No. 5,701,348, entitled "Articulated Hearing Device" ("the '348 patent"), discloses a segmented hearing device with several articulating and non-contiguous parts. The hearing device disclosed in the '348 patent includes a rigid receiver module with a surrounding acoustic seal. The acoustic seal formed by the hearing device disclosed '348 patent includes a sheathing made from a singular piece of foam or silicone which compresses when inserted into the deep regions of an ear canal. The '348 patent also describes the use of this sealing mechanism as an anchor so that the remaining articulating components of the hearing device can move freely and adjust to the changing morphology of the ear canal. While generally conforming to the shape of an ear canal, the hearing device disclosed in the '348 patent still presents comfort problems during insertion and removal due to the single piece construction of its sealing mechanism. Also, due to the single piece construction, the quality of the acoustic seal degrades over time and during prolonged use. Further, the ability to effectively interchange and clean the sealing material is also compromised. In particular, the device disclosed in the '348 patent is not conducive to use with a CIC hearing device, where the acoustic seal is the only point of contact with the ear canal. Compression of the sealing material reduces the volume of the foam and the sealing properties are accordingly diminished.
U.S. Pat. No. 5,395,168, entitled "In the Ear Hearing Aid Having Extraction Tube Which Reduces Acoustic Feedback" ("the '168 patent"), discloses an in-the-ear hearing device, which incorporates a retrieval system mechanically attached to the hearing device body. The retrieval cord is also presented as a hollow acoustic tube to aid in reducing acoustic feedback. In order to reduce acoustic feedback, the acoustic tube disclosed in the '168 patent extends into the receiver housing and engages with the receiver elements. While aiding in the reduction of acoustic interference, this device also presents comfort problems during insertion and removal due to the lack of a venting or pressure equalization system between the inner chamber formed by the hearing device, and the ambient environment.
U.S. Pat. No. 4,880,076, entitled "Hearing Aid Ear Piece Having Disposable Compressible Polymeric Foam Sleeve" ("the '076 patent"), discloses a disposable sleeve that is secured to the ear piece of a hearing aid. The sleeve includes a plastic duct which is fitted with a threaded connection for attachment to the hearing aid ear piece. A soft polymeric foam piece is placed over the sleeve. While the duct disclosed in the '076 patent does provide venting capabilities, the rigid structure and threaded or snap connections add significant size to the hearing aid tip. In particular, the device disclosed in the '076 patent still requires a separate retrieval cord for smaller hearing aid tips. Even though the duct and foam covered sleeve are soft and flexible, the threaded connectors are not, and contribute to an overall lack of flexibility of the device.